Okay, I'm still not completely sure what you are saying, so let me try to summarize in my own words:
You have a Lite-On LTR-48246S 48x CD-RW drive, and it had been running fine. You could both read and write at 48x CAV. Then you ran CD Speed to test the writing speed for a blank CD-R. Because the CD-R was low quality, the drive reduced its writing speed to 14.5x CLV. Now when you test this same disc with CD Speed's Transfer Rate test to see the read speed, it remains "stuck" at 14.5x CLV. Other discs you wrote before the problem surfaced are now also stuck at 14.5x CLV.
First of all, when you run CD Speed's Transfer Rate test (F2) on a blank CD, it doesn't actually write data. So if you put the same disc back in the drive after the "write" test and run the Transfer Rate test again thinking you are now testing the read speed, you aren't. Instead you are running the write speed transfer rate test again. That would be one explanation for part of the behavior you are seeing.
However, I assume that this is not what you did, and that you actually ran the Create Data CD test (F9) as the original test. Based on this, the fact that 14.5x is not a supported write speed, and the fact that all your other discs also read at 14.5x, I think the most likely explanation for what you are seeing is that Windows detected some troubles on the IDE bus and disabled DMA for your CD-RW drive. Windows XP is known to do this. What is your CPU usage when reading and writing with the drive? Check the [url=http://www.cdrlabs.com/phpBB/viewtopic.php?t=7625]How to enable DMA in Windows XP (with pictures)
[/url] and Problems enabling DMA in Windows XP
FAQs for tips on restoring DMA.